Exogenous Salicylic Acid Research Articles

Salicylic Acid Alleviates Aluminum Toxicity in Soybean Roots through Modulation of Reactive Oxygen Species Metabolism.

As an important signal molecule, salicylic acid (SA) improves plant tolerance to aluminum (Al) stress. The objective of this study was to investigate the effects of exogenous SA application on the dynamics of endogenous SA and reactive oxygen species in soybean (Glycine max L.) exposed to Al stress. The roots of soybean seedlings were exposed to a combination of AlCl3 (30 μM) and SA (10 μM)/PAC (100 μM, paclobutrazol, SA biosynthesis inhibitor) for 3, 6, 9, and 12 h. Al stress induced an increase in endogenous SA concentration in a time-dependent manner, also verified by the up-regulated expression of GmNPR1, an SA-responsive gene. Al stress increased the activities of phenylalanine ammonia-lyase (PAL) and benzoic acid 2-hydroxylase (BA2H), and the contents of SA, and malondialdehyde (MDA) in the root apex. The application of exogenous SA increased PAL and BA2H, and reduced and MDA contents in soybean roots under Al stress. PAC inhibited the SA induced increase in BA2H activity. In addition, the SA application resulted in a rapid increase in hydrogen peroxide (H2O2) concentration under Al stress, followed by a sharp decrease. Compared with the plants exposed to Al alone, Al+SA plants possessed higher activities of superoxide dismutase, peroxidase, and ascorbate peroxidase, and lower catalase activity, indicating that SA alleviated Al-induced oxidative damage. These results suggested that PAL and BA2H were involved in Al-induced SA production and showed that SA alleviated the adverse effects of Al toxicity by modulating the cellular H2O2 level and the antioxidant enzyme activities in the soybean root apex.

Synergistic effects of plant defense elicitors and Trichoderma harzianum on enhanced induction of antioxidant defense system in tomato against Fusarium wilt disease

Plant defense against their pathogens can be induced by a complex network of different inducers. The present study investigates the synergistic effect of Trichoderma harzianum, exogenous salicylic acid (SA) and methyl jasmonate (MeJA) over the response and regulation of the antioxidant defense mechanisms and lipid peroxidation in tomato plants against Fusarium wilt disease. In the present work, tomato plants were infected by Fusarium oxysporum f. sp. lycopersici 3 days after inoculated with T. harzianum and/or sprayed daily for 3 days with chemical inducers (SA and MeJA). Plants were analysed at 0, 24, 48, 72 and 96 h after inoculation with Fusarium oxysporum f. sp. lycopersici. Infection of tomato plants by pathogen led to strong reduction in the dry weight of roots and shoots with the enhanced concentration of H2O2 and varying degree of lipid peroxidation. Concurrently, exogenous SA, when applied with pathogen greatly enhanced H2O2 content as well as activities of antioxidant enzymes except catalase (CAT) and ascorbate peroxidase (APx). The pathogen challenged plants pretreated with T. harzianum and MeJA together exhibited less lipid peroxidation and as well as the elevated level of ascorbic acid and enhanced activities of antioxidant enzymes. All applied treatments protected tomato seedlings against Fusarium wilt disease but the percentage of protection was found higher in plants pretreated with the combination of T. harzianum and chemical inducers.

Members of the abscisic acid co-receptor PP2C protein family mediate salicylic acid-abscisic acid crosstalk.

The interplay between abscisic acid (ABA) and salicylic acid (SA) influences plant responses to various (a)biotic stresses; however, the underlying mechanism for this crosstalk is largely unknown. Here, we report that type 2C protein phosphatases (PP2Cs), some of which are negative regulators of ABA signaling, bind SA. SA binding suppressed the ABA‐enhanced interaction between these PP2Cs and various ABA receptors belonging to the PYR/PYL/RCAR protein family. Additionally, SA suppressed ABA‐enhanced degradation of PP2Cs and ABA‐induced stabilization of SnRK2s. Supporting SA's role as a negative regulator of ABA signaling, exogenous SA suppressed ABA‐induced gene expression, whereas the SA‐deficient sid2‐1 mutant displayed heightened PP2C degradation and hypersensitivity to ABA‐induced suppression of seed germination. Together, these results suggest a new molecular mechanism through which SA antagonizes ABA signaling. A better understanding of the crosstalk between these hormones is important for improving the sustainability of agriculture in the face of climate change.

Exogenous salicylic acid improves freezing tolerance of spinach (Spinacia oleracea L.) leaves

Salicylic acid (SA)-treatment has been reported to improve plant tolerance to various abiotic stresses. However, its effect on freezing tolerance has not been well investigated. We investigated the effect of exogenous SA on freezing tolerance of spinach (Spinacia oleracea L.) leaves. We also explored if nitric oxide (NO) and/or hydrogen peroxide (H2O2)-mediation was involved in this response, since these are known as primary signaling molecules involved in many physiological processes. A micro-centrifuge tube-based system used to apply SA to petiolate spinach leaves (0.5 mM over 4-d) was effective, as evident by SA content of leaf tissues. SA-treatment did not hamper leaf growth (fresh and dry weight; equatorial and longitudinal length) and was also not significantly different from 25% Hoagland controls vis-à-vis growth. SA application significantly improved freezing tolerance as evidenced by reduced ion-leakage and alleviated oxidative stress (lower accumulation of O2·- and H2O2) following freeze-thaw stress treatments (−6.5, −7.5, and −8.5 °C). Improved freezing tolerance of SA-treated leaves was paralleled by increased proline and ascorbic acid (AsA) accumulation. A 9-d cold acclimation (CA) treatment also improved leaf freezing tolerance (compared to non-acclimated control) and was accompanied by accumulation of SA and proline. Our results indicate that increased freezing tolerance may be associated with accumulation of compatible solutes (proline) and antioxidants (AsA). Notably, the beneficial effect of SA on freezing tolerance was abolished when either H2O2- or NO-scavenger (1 μM N-acetylneuraminic acid, NANA or 100 μM hemoglobin, HB, respectively) was added to SA as pretreatment. Our data suggest that SA-induced freezing tolerance in spinach may be mediated by NO and H2O2 signaling.

Effects of exogenous salicylic acid on seed germination and physiological characteristics of Coronilla varia under drought stress.

This research investigated the effects of different concentrations (0, 0.5, 1.0, 2.0 mmol·L-1) of salicylic acid on the seed germination and physiological characteristics of legume forage Coronilla varia (cultivar 'Lvbaoshi') under PEG-6000 (concentration 8% and 12%) simulated drought stress. The results showed that under drought stress, 0.5-1.0 mmol·L-1 salicylic acid significantly increased germination percentage, germination vigour, germination index, vitality index and bud length of C. varia. Under the stress of 12% PEG, the dry mass of C. varia seedlings processed by 1.0 mmol·L-1 salicylic acid was significantly higher than that under drought stress. 0.5-1.0 mmol·L-1 salicylic acid processing significantly increased proline, soluble protein content, the activities of catalase, peroxidase and superoxide dismutase of C. varia seedlings under drought stress, but cell electrolyte permeability, H2O2 content and O2-· production rate of seedlings were significantly decreased. 1.0 mmol·L-1 salicylic acid produced the best results. When the concentration of salicylic acid was beyond 2.0 mmol·L-1, no mitigation effect was observed on the seed germination and growth of seedlings under drought stress. It was concluded that salicylic acid at appropriate concentrations could effectively improve osmotic regulation, antioxidation and mitigate the damage of drought stress so as to promote the growth of C. varia seedlings.

Alleviation of cadmium toxicity in Lemna minor by exogenous salicylic acid

Cadmium (Cd) is a significant environmental pollutant in the aquatic environment. Salicylic acid (SA) is a ubiquitous phenolic compound. The goal of this study was to assess the morphological, physiological and biochemical changes in duckweed (L. minor) upon exposure to 10μM CdCl2, 10μM CdCl2 plus 50μM SA, or 50μM SA for 7 days. Reversing the effects of Cd, SA decreased Cd accumulation in plants, improved accumulation of minerals (Ca, Mg, Fe, B, Mo) absorption, increased endogenous SA concentration, and phenylalanine ammonialyase (PAL) activity. Chlorosis-associated symptoms, the reduction in chlorophyll content, and the overproduction of reactive oxygen species induced by Cd exposure were largely reversed by SA. SA significantly decreased the toxic effects of Cd on the activities of the superoxide dismutase, peroxidase, catalase, ascorbate peroxidase, and glutathione reductase in the fronds of L. minor. Furthermore, SA reversed the detrimental effects of Cd on total ascorbate, glutathione, the ascorbic acid/oxidized dehydroascorbate and glutathione/glutathione disulphide ratios, lipid peroxidation, malondialdehyde concentration, lipoxygenase activity, and the accumulation of proline. SA induced the up-regulation of heat shock proteins (Hsp70) and attenuated the adverse effects of Cd on cell viability. These results suggest that SA confers tolerance to Cd stress in L. minor through different mechanisms.

Expression of PR genes in tomato tissues infected by nematode Meloidogyne incognita (Kofoid et White, 1919) Chitwood, 1949.

The dynamics of expression of PR1 and PR6 genes, which are involved in the defense response of plants infected with the root-knot nematode Meloidogyne incognita, was studied in the "tomato-root-knot nematode" parasitic system. The invasion of the resistant plants was accompanied by an increased accumulation of transcripts of PR genes, which reflects their fast response to the penetration of nematode juveniles with subsequent development of an adequate defense response. In the susceptible plants, changes in the PR1 and PR6 gene activity induced by the nematode invasion were insignificant, which may be one of the causes of the disease. An exogenous salicylic acid treatment of the susceptible plants increased the PR1 and PR6 genes activity and led to the development of resistance of these plants to nematode invasion.

In Vitro Induced Resistance of Fusarium Wilt Disease (Fusarium oxysporum f.sp. cepae) by Salicylic Acid in Shallot CV ‘Bima Brebes’

Fusarium wilt caused by Fusarium oxysporum f.sp.cepae (Foc) is one of the most important diseases of onion in Indonesia. Induced resistance was one of the effective techniques to acquire resistance to fusarium wilt in shallot. Salicylic acid (SA) had been inferred to be in endogenous signal in the systemic acquired resistance response of plants. This research aimed to study the effect of exogenously added SA to resistance in shallot callus cv ‘Bima Brebes’ to fusarium wilt disease in vitro; and to determine the effective concentration of SA to induce resistance. A group of shallot callus was grown in MS medium containing varying SA concentration (0, 15, 20 and 25 ppm) in vitro for 2 weeks. Then, the callus were treated with toxin of Fusarium oxysporum, namely fusaric acid, to have observe the resistance response. In vitro selection was done twice in different fusaric acid concentration. Application of exogenous SA at all concentration did not suppres time of appearance of disease symptom yet. Toxic symptom in the callus was shown by the browning or blackening (off) of callus. Salicylic acid at concentration of 20 ppm effectively reduced the toxic symptom up to 16.66% and supported callus regeneration better than the concentration of 15 ppm and 25 ppm. The number of resistant callus regenerated was 66.67% at pretreatment of 20 ppm of SA.

Chitosan signaling in guard cells requires endogenous salicylic acid.

An elicitor chitosan (CHT) induces stomatal closure but the mechanism remains to be clarified. A phytohormone salicylic acid (SA) is crucial for elicitor-induced defense signaling in plants. Here we investigated whether endogenous SA is required for CHT signaling in guard cells. In the SA-deficient nahG mutant, treatment of CHT did not induce either apoplastic reactive oxygen species (ROS) production or stomatal closure but co-treatment of CHT and SA induced both apoplastic ROS production and stomatal closure, indicating the involvement of endogenous SA in CHT-induced apoplastic ROS production and CHT-induced stomatal closure. Furthermore, CHT induced transient cytosolic free calcium concentration increments in the nahG mutant in the presence of exogenous SA but not in the absence of exogenous SA. These results provide evidence that endogenous SA is a crucial element in CHT-induced stomatal closure.

A rapid and efficient Agrobacterium-mediated transient gene expression system for strawberry leaves and the study of disease resistance proteins

Transient gene expression is a simple and universal method and has been broadly applied in gene functional analyses in several plant species. However, few studies have reported the utilization and transient expression of strawberry leaves. Here, an Agrobacterium-mediated transient gene expression system was established in strawberry leaves. The strawberry leaf transient gene expression system was tested for protein expression, western blot assays, and protein subcellular localization. Furthermore, the Arabidopsis thaliana broad-spectrum disease resistance protein RPW8.2 was transiently expressed in strawberry leaves. Both the application of exogenous salicylic acid (SA) and the following infection by the strawberry powdery mildew pathogen, Podosphaera aphanis, resulted in increased expression of the RPW8.2 fusion protein. Reverse transcription quantitative PCR analysis showed that the transient expression of AtRPW8.2 in strawberry leaves could induce defense-related gene transcription levels. In conclusion, we demonstrated the potential of a rapid and efficient Agrobacterium-mediated transient gene expression system in strawberry leaves and its use for the study of disease resistant protein activity in strawberry leaves.

The Phenylalanine Ammonia Lyase Gene LjPAL1 Is Involved in Plant Defense Responses to Pathogens and Plays Diverse Roles in Lotus japonicus-Rhizobium Symbioses.

Phenylalanine ammonia lyase (PAL) is important in the biosynthesis of plant secondary metabolites that regulate growth responses. Although its function is well-established in various plants, the functional significance of PAL genes in nodulation is poorly understood. Here, we demonstrate that the Lotus japonicus PAL (LjPAL1) gene is induced by Mesorhizobium loti infection and methyl-jasmonate (Me-JA) treatment in roots. LjPAL1 altered PAL activity, leading to changes in lignin contents and thicknesses of cell walls in roots and nodules of transgenic plants and, hence, to structural changes in roots and nodules. LjPAL1-knockdown plants (LjPAL1i) exhibited increased infection thread and nodule numbers and the induced upregulation of nodulin gene expression after M. loti infection. Conversely, LjPAL1 overexpression delayed the infection process and reduced infection thread and nodule numbers after M. loti inoculation. LjPAL1i plants also exhibited reduced endogenous salicylic acid (SA) accumulation and expression of the SA-dependent marker gene. Their infection phenotype could be partially restored by exogenous SA or Me-JA application. Our data demonstrate that LjPAL1 plays diverse roles in L. japonicus-rhizobium symbiosis, affecting rhizobial infection progress and nodule structure, likely by inducing lignin modification, regulating endogenous SA biosynthesis, and modulating SA signaling.

The Synergistic Priming Effect of Exogenous Salicylic Acid and H2O2 on Chilling Tolerance Enhancement during Maize (Zea mays L.) Seed Germination.

Chilling stress is an important constraint for maize seedling establishment in the field. To examine the role of salicylic acid (SA) and hydrogen peroxide (H2O2) in response to chilling stress, we investigated the effects of seed priming with SA, H2O2, and SA+H2O2 combination on maize resistance under chilling stress (13°C). Priming with SA, H2O2, and especially SA+H2O2 shortened seed germination time and enhanced seed vigor and seedling growth as compared with hydropriming and non-priming treatments under low temperature. Meanwhile, SA+H2O2 priming notably increased the endogenous H2O2 and SA content, antioxidant enzymes activities and their corresponding genes ZmPAL, ZmSOD4, ZmAPX2, ZmCAT2, and ZmGR expression levels. The α-amylase activity was enhanced to mobilize starch to supply metabolites such as soluble sugar and energy for seed germination under chilling stress. In addition, the SA+H2O2 combination positively up-regulated expressions of gibberellic acid (GA) biosynthesis genes ZmGA20ox1 and ZmGA3ox2, and down-regulated GA catabolism gene ZmGA2ox1 expression; while it promoted GA signaling transduction genes expressions of ZmGID1 and ZmGID2 and decreased the level of seed germination inhibitor gene ZmRGL2. The abscisic acid (ABA) catabolism gene ZmCYP707A2 and the expressions of ZmCPK11 and ZmSnRK2.1 encoding response receptors in ABA signaling pathway were all up-regulated. These results strongly suggested that priming with SA and H2O2 synergistically promoted hormones metabolism and signal transduction, and enhanced energy supply and antioxidant enzymes activities under chilling stress, which were closely relevant with chilling injury alleviation and chilling-tolerance improvement in maize seed.Highlights:Seed germination and seedling growth were significantly improved under chilling stress by priming with SA+H2O2 combination, which was closely relevant with the change of reactive oxygen species, metabolites and energy supply, hormones metabolism and regulation.

Exogenous Salicylic Acid-Mediated Physiological Responses and Improvement in Yield by Modulating Antioxidant Defense System of Wheat under Salinity

Present study investigates the regulatory roles of exogenous salicylic acid (SA) in physiology, antioxidant defense systems and yield of wheat under different salt stress condition. The experiment was conducted with two varieties i.e. BARIGom 21 and BARIGom 25 and ten salt stress treatments viz. control (without salt), SA (1 mMsalicylic acid), S50 (50 mMsalt stress), S50+SA (50 mMsalt stress with 1 mMSA), S100 (100 mMsalt stress), S100+SA (100 mMsalt stress with 1 mMSA), S150 (150 mMsalt stress), S150+SA (150 mMsalt stress with 1 mMSA), S200 (200 mMsalt stress) and S200+SA (200 mMsalt stress with 1 mMSA). Leaf relative water content (RWC) and chlorophyll (chl) content reduced due to salt stress. The malondialdelyde (MDA) and H2O2 were increased under the stress condition. The ascorbate (AsA) content, reduced glutathione (GSH) and GSH/GSSG ratio were reduced by salt stresses (50, 100, 150 and 200 mM, respectively). But the glutathione disulfide (GSSG) amount increased with an increase in the all level of salinity. The ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR) and catalase (CAT) activities showed a significant reduction in response to salt stress but CAT increased only at 100 mM stress condition. The glutathione S-transferase (GST) and glutathione reductase (GR) activity increased significantly with severe salt stress (200 mM). But the activity of peroxidase (POD) was decreased with increasing salinity level. At harvest, salt stresses reduced the effective tiller hill-1, 1000 grain weight, grain yield, straw yield, biological yield and harvest index for both of varieties. However, number of non-effective tiller hill-1 significantly increased in response of salt stress. Exogenous 1 mM SA application with salt stress improved physiological parameters, yield and reduced oxidative damage in both cultivars whereBARI Gom 25 showed better tolerance. But, SA application could not improve physiological parameters and yield at extreme level of salt stress (200 mM).

Effect of exogenous salicylic acid and ultraviolet radiation on Ulva prolifera under different light conditions

To study the combined effects of exogenous salicylic acid (SA) and ultraviolet radiation (UV) on marine green algae Ulva prolifera under high (160 Μmol·m-2·s-1) and low (70 Μmol·m-2·s-1) light intensities, the growth, chlorophyll fluorescence parameters, photosynthetic rate of oxygen, superoxide dismutase (SOD) activity, soluble polysaccharide and soluble protein contents were investigated after they grew with or without ultraviolet (UV, 3.2 W·m-2) radiation in the presence or absence of SA (10 Μg·mL-1) for three days. The treatments included control group (CK), SA, UV and UV+SA treatments. Results showed that under the low light intensity without UV condition, the relative growth rate was enhanced, Chl a and soluble protein contents were decreased by SA. Under the high light intensity without UV condition, the relative growth rate was decreased, Chl a content, respiratory rate, photosynthetic rate of oxygen, soluble polysaccharide and soluble protein contents were enhanced by SA. Under the high light intensity with UV condition, the relative growth rate, Chl a and soluble polysaccharide contents were enhanced by UV+SA. Additionally, under the low light intensity with UV condition, compared to UV treatment, the maximum photochemical efficiency (Fv/Fm) and soluble protein contents were respectively increased by 139.8% and 32.2% under the UV+SA treatment. In conclusion, SA reduced the inhibitory effects of U. prolifera induced by UV, and the effects were more significant under the high light intensity.

‘Candidatus Liberibacter asiaticus’ Encodes a Functional Salicylic Acid (SA) Hydroxylase That Degrades SA to Suppress Plant Defenses

Pathogens from the fastidious, phloem-restricted 'Candidatus Liberibacter' species cause the devastating Huanglongbing (HLB) disease in citrus worldwide and cause diseases on many solanaceous crops and plants in the Apiaceae family. However, little is known about the pathogenic mechanisms due to the difficulty in culturing the corresponding 'Ca. Liberibacter' species. Here, we report that the citrus HLB pathogen 'Ca. L. asiaticus' uses an active salicylate hydroxylase SahA to degrade salicylic acid (SA) and suppress plant defenses. Purified SahA protein displays strong enzymatic activity to degrade SA and its derivatives. Overexpression of SahA in transgenic tobacco plants abolishes SA accumulation and hypersensitive response (HR) induced by nonhost pathogen infection. By degrading SA, 'Ca. L. asiaticus' not only enhances the susceptibility of citrus plants to both nonpathogenic and pathogenic Xanthomonas citri but also attenuates the responses of citrus plants to exogenous SA. In addition, foliar spraying of 2,1,3-benzothiadiazole and 2,6-dichloroisonicotinic acid, SA functional analogs not degradable by SahA, displays comparable (and even better) effectiveness with SA in suppressing 'Ca. L. asiaticus' population growth and HLB disease progression in infected citrus trees under field conditions. This study demonstrates one or more pathogens suppress plant defenses by degrading SA and establish clues for developing novel SA derivatives-based management approaches to control the associated plant diseases.

Exogenous salicylic acid alleviates salt-stress damage in cucumber under moderate nitrogen conditions by controlling endogenous salicylic acid levels

Salicylic acid (SA) is a signaling compound that plays an important role in plant responses to biotic and abiotic stress. Exogenous application of SA can improve abiotic stress tolerance in various plants, a response that varies depending on the nutrient status of the plant. Based on the hypothesis that the nutrient status of a plant affects SA-induced stress tolerance, we investigated SA-induced stress tolerance in cucumber grown under moderate nitrogen (MN, 120 ppm) and low nitrogen (LN, 40 ppm) conditions. Cucumbers grown under MN conditions showed SA-induced tolerance to salt stress, along with mild increases in endogenous SA levels. In cucumbers without SA pretreatment, the increase in endogenous SA levels after salt stress treatment was approximately 2-fold higher than that of SA-pretreated plants. On the other hand, exogenous SA did not increase salt-stress tolerance in plants grown in LN exhibiting leaf chlorosis, although SA levels increased in the leaves of these plants. These results indicate that exogenous SA-induced salt stress tolerance is well established in cucumber grown in MN. In addition, SA pretreatment can improve the ability of plants to regulate endogenous SA levels after salt stress when grown under suitable nutrient conditions.

The salicylic acid analog 2,6-dichloroisonicotinic acid has specific impact on the response of the halophyte plant species Solanum chilense to salinity

Salicylic acid (SA) is involved in the salt-resistance of the halophyte plant species Solanum chilense. The SA analog 2,6-dichloroisonicotinc acid (INA) is commonly used to elicit SA signal transduction in response to biotic stress and is frequently used to confirm the SA involvement in plant response to pathogens. Data are lacking concerning its impact on plant response to salinity, especially in the halophyte species. Solanum chilense was cultivated in the absence or presence of 125 mM NaCl in nutrient solution and exposed to 0.01 mM exogenous SA or sprayed with 0.5 mM INA. Exogenous SA increased the shoot dry weight while INA did not. Exogenous INA, in contrast to SA, increased the shoot Na+ concentration in NaCl-treated plants and decreased the root K+ concentration. In the absence of salt, both SA and INA induced an increase in H2O2 which was not due to ascorbate peroxidase (EC 1.11.1.11) inhibition. In salt-treated plants, SA stimulated the ascorbate peroxidase activity while INA did not. Exogenous SA increased the root putrescine and spermidine concentrations while INA significantly decreased the concentration of these protecting compounds. It is concluded that exogenous SA and INA do not have similar impacts on the plant behavior and that the difference between these compounds may be influenced by NaCl. The use of INA as a reliable SA analog should therefore be considered with caution in halophyte plant species.

Genome-wide analysis of autophagy-related genes in banana highlights MaATG8s in cell death and autophagy in immune response to Fusarium wilt.

MaATG8s play important roles in hypersensitive-like cell death and immune response, and autophagy is essential for disease resistance against Foc in banana. Autophagy is responsible for the degradation of damaged cytoplasmic constituents in the lysosomes or vacuoles. Although the effects of autophagy have been extensively revealed in model plants, the possible roles of autophagy-related gene in banana remain unknown. In this study, 32 MaATGs were identified in the draft genome, and the profiles of several MaATGs in response to fungal pathogen Fusarium oxysporum f. sp. cubense (Foc) were also revealled. We found that seven MaATG8s were commonly regulated by Foc. Through transient expression in Nicotiana benthamiana leaves, we highlight the novel roles of MaATG8s in conferring hypersensitive-like cell death, and MaATG8s-mediated hypersensitive response-like cell death is dependent on autophagy. Notablly, autophagy inhibitor 3-methyladenine (3-MA) treatment resulted in decreased disease resistance in response to Foc4, and the effect of 3-MA treatment could be rescued by exogenous salicylic acid, jasmonic acid and ethylene, indicating the involvement of autophagy-mediated plant hormones in banana resistance to Fusarium wilt. Taken together, this study may extend our understanding the putative role of MaATG8s in hypersensitive-like cell death and the essential role of autophagy in immune response against Foc in banana.

Salicylic Acid Alleviates the Adverse Effects of Salt Stress on Dianthus superbus (Caryophyllaceae) by Activating Photosynthesis, Protecting Morphological Structure, and Enhancing the Antioxidant System.

Salt stress critically affects the physiological processes and morphological structure of plants, resulting in reduced plant growth. Salicylic acid (SA) is an important signal molecule that mitigates the adverse effects of salt stress on plants. Large pink Dianthus superbus L. (Caryophyllaceae) usually exhibit salt-tolerant traits under natural conditions. To further clarify the salt-tolerance level of D. superbus and the regulating mechanism of exogenous SA on the growth of D. superbus under different salt stresses, we conducted a pot experiment to examine the biomass, photosynthetic parameters, stomatal structure, chloroplast ultrastructure, reactive oxygen species (ROS) concentrations, and antioxidant activities of D. superbus young shoots under 0.3, 0.6, and 0.9% NaCl conditions, with and without 0.5 mM SA. D. superbus exhibited reduced growth rate, decreased net photosynthetic rate (Pn), increased relative electric conductivity (REC) and malondialdehyde (MDA) contents, and poorly developed stomata and chloroplasts under 0.6 and 0.9% salt stress. However, exogenously SA effectively improved the growth, photosynthesis, antioxidant enzyme activity, and stoma and chloroplast development of D. superbus. However, when the plants were grown under severe salt stress (0.9% NaCl condition), there was no significant difference in the plant growth and physiological responses between SA-treated and non-SA-treated plants. Therefore, our research suggests that exogenous SA can effectively counteract the adverse effect of moderate salt stress on D. superbus growth and development.

Interactive effects of Salicylic acid and nitric oxide in alleviating zinc toxicity of Safflower (Carthamus tinctorius L.)

The purpose of this study was to assess the possible protective role of exogenous salicylic acid (SA), sodium nitroprusside (SNP), a donor of nitric oxide, and their combination on 21-day-old safflower (Carthamus tinctorius L.) seedlings grown under zinc (Zn) stress. The results revealed that exposure to 500 µM ZnSO4.7H2O for 10 days markedly reduced the root and shoot dry weights in Zn-treated plants, while the application of SA, SNP and specially SA + SNP significantly increased the root and shoot dry weights in seedlings subjected to Zn stress. Addition of SA, SNP and SA + SNP interestingly reduced root-to-shoot translocation of zinc and increased significantly the level of glutathione (GSH) and ascorbate (ASC) in leaves of Zn-stressed plants. The Zn-treated plants supplemented with SA and SNP revealed an improved activity of ascorbate-glutathione cycle enzymes and those enzymes which are involved in glyoxalase system as compared to the plants treated with Zn only. However, no significant relationship was found between SA or SNP supplementation and glutathione S-transferase activity in Zn-stressed plants. These findings demonstrate that exogenous application of SA or SNP could ameliorate the negative effects of Zn on safflower plants probably by stimulation of antioxidant defense and glyoxalase systems.